The centromere is a chromatin region that serves as the spindle attachment point and directs accurate inheritance of eukaryotic chromosomes during cell divisions. However, the mechanism by which the centromere assembles and stabilizes at a specific genomic region is not clear. The de novo formation of a human/mammalian artificial chromosome (HAC/MAC) with a functional centromere assembly requires the presence of alpha-satellite DNA containing binding motifs for the centromeric CENP-B protein. We demonstrate here that de novo centromere assembly on HAC/MAC is dependent on CENP-B. In contrast, centromere formation is suppressed in cells expressing CENP-B when alpha-satellite DNA was integrated into a chromosomal site. Remarkably, on those integration sites CENP-B enhances histone H3-K9 trimethylation and DNA methylation, thereby stimulating heterochromatin formation. Thus, we propose that CENP-B plays a dual role in centromere formation, ensuring de novo formation on DNA lacking a functional centromere but preventing the formation of excess centromeres on chromosomes.

Animals, including humans, express two isoforms of acetyl-CoA carboxylase (EC 6.4.1.2), ACC1 (Mr ‫؍‬ 265 kDa) and ACC2 (Mr ‫؍‬ 280 kDa). The predicted amino acid sequence of ACC2 contains an additional 136 aa relative to ACC1, 114 of which constitute the unique N-terminal sequence of ACC2. The hydropathic profiles of the two ACC isoforms generally are comparable, except for the unique N-terminal sequence in ACC2. The sequence of amino acid residues 1-20 of ACC2 is highly hydrophobic, suggesting that it is a leader sequence that targets ACC2 for insertion into membranes. The subcellular localization of ACC2 in mammalian cells was determined by performing immunofluorescence microscopic analysis using affinity-purified anti-ACC2-specific antibodies and transient expression of the green fluorescent protein fused to the C terminus of the N-terminal sequences of ACC1 and ACC2. These analyses demonstrated that ACC1 is a cytosolic protein and that ACC2 was associated with the mitochondria, a finding that was confirmed further by the immunocolocalization of a known human mitochondria-specific protein and the carnitine palmitoyltransferase 1. Based on analyses of the fusion proteins of ACC-green fluorescent protein, we concluded that the N-terminal sequences of ACC2 are responsible for mitochondrial targeting of ACC2. The association of ACC2 with the mitochondria is consistent with the hypothesis that ACC2 is involved in the regulation of mitochondrial fatty acid oxidation through the inhibition of carnitine palmitoyltransferase 1 by its product malonyl-CoA.A cetyl-CoA carboxylase (ACC) catalyzes the carboxylation of acetyl-CoA to form malonyl-CoA, an intermediate substrate that plays a pivotal role in the regulation of fatty acid metabolism. Besides its role in the biosynthesis of long-chain fatty acids (1-3), malonyl-CoA has been implicated in the regulation of the carnitine palmitoyl-CoA shuttle system that is involved in the mitochondrial ␤-oxidation of long-chain fatty acids. In animals, two isoforms of the carboxylase have been identified, ACC1 (M r ϭ 265,000) and ACC2 (M r ϭ 280,000) (4, 5). The two enzymes are encoded by separate genes and display distinct tissue distribution and regulation (6-9). The ACC1 carboxylases are highly expressed in lipogenic tissues, such as liver and adipose, and their levels are regulated transcriptionally while their activities are regulated posttranslationally by phosphorylation͞dephosphorylation of selected serine residues and by allosteric regulation through the action of citrate and palmitoyl-CoA (10-18). Dietary and hormonal states of the animal affect the level and activities of the ACC1 enzymes. A carbohydrate-rich, low-fat diet stimulates the expression and activities of ACC1, whereas starvation and diabetes reduce the ACC1 activities by repressing the expression of the ACC1 gene or by increasing the phosphorylation levels of the ACC1 protein (or both). Treating diabetic animals with insulin increases the activity of the enzyme either by dephosphorylation of the protein or by...

The function of Aurora-C kinase, a member of the Aurora kinase family identified in mammals, is currently unknown. We present evidence that Aurora-C, like Aurora-B kinase, is a chromosomal passenger protein localizing first to centromeres and then to the midzone of mitotic cells. Aurora-C transcript is expressed at a moderate level albeit about an order of magnitude lower than Aurora-B transcript in diploid human fibroblasts. The level of Aurora-C transcript is elevated in several human cancer cell types. Aurora-C and Aurora-B mRNA and protein expressions are maximally elevated during the G2/M phase but their expression profiles in synchronized cells reveal differential temporal regulation through the cell cycle with Aurora-C level peaking after that of Aurora-B during the later part of the M phase. Aurora-C, like Aurora-B, interacts with the inner centromere protein (INCENP) at the carboxyl terminal end spanning the conserved IN box domain. Competition binding assays and transfection experiments revealed that, compared with Aurora-C, Aurora-B has preferential binding affinity to INCENP and co-expression of the two in vivo interferes with INCENP binding, localization, and stability of these proteins. A kinase-dead mutant of Aurora-C had a dominant negative effect inducing multinucleation in a dose-dependent manner. siRNA mediated silencing of Aurora-C and Aurora-B also gave rise to multinucleated cells with the two kinases silenced at the same time displaying an additive effect. Finally, Aurora-C could rescue the Aurora-B silenced multinucleation phenotype, demonstrating that Aurora-C kinase function overlaps with and complements Aurora-B kinase function in mitosis.

STK15 gene amplification and associated increased expression of the mitotic kinase it encodes are associated with aneuploidy and aggressive clinical behavior in human bladder cancer.

Mitosin is a novel 350-kDa nuclear phosphoprotein that dramatically relocates from the evenly nuclear distribution in S phase to the centromere/kinetochore and mitotic apparatus in M phase. The dynamic relocalization of mitosin is accompanied by the phosphorylation of itself, suggesting that mitosin plays a role in mitotic progression. The molecular basis of nuclear localization and targeting of mitosin to the centromere/kinetochore were characterized using a set of epitope-tagged deletion mutants. The data indicate that the extreme C terminus (amino acids 2,487-3,113) of mitosin has both an independent centromere/kinetochore targeting domain and an unusually spaced bipartite nuclear localization signal. Moreover, the same centromere/kinetochore targeting domain was shown to be essential for the ability of mitosin to bind to itself or other putative mitosin-associated proteins through use of the yeast two-hybrid system. These results suggest that the C terminus of the mitosin is essential for its role in influencing cell cycle progression.

Aurora kinases representing a novel family of serine/threonine kinases have been identified as key regulators of the mitotic cell division process. The three members of this kinase family, identified so far, referred to as Aurora-A, Aurora-B and Aurora-C kinases, are close homologues of the prototypic yeast Ipll and Drosophila aurora kinases, which are known to be involved in the regulation of centrosome function, bipolar spindle assembly and chromosome segregation processes. All three members of the mammalian kinase family have a catalytic domain that is highly conserved with a short C-terminal domain and an N-terminal domain of varying sizes. Following their discovery about five years ago, extensive research has focused on understanding the biological roles of these kinases and elucidation of their pathways, which regulate cell proliferation and maintenance of normal cellular phenotypes. Significant interest in the subject was generated since all three Aurora kinases family members were reported to be overexpressed in many human cancers, and elevated expression has been correlated with chromosomal instability and clinically aggressive disease in some instances. Ectopic overexpression of one member of the family, Aurora-A, was shown to induce oncogenic transformation in cells. Unlike most other putative oncogenes identified, so far, members of this kinase family are expressed and active at the highest level during G2-M phase of the cell cycle. Aurora kinases are localized at the centrosomes of interphase cells, at the poles of the bipolar spindle and in the midbody of the mitotic apparatus. Substrates identified for the Aurora-A and Aurora-B kinases, include a kinesin-like motor protein, spindle apparatus proteins, histone H3 protein, kinetochore protein and the tumor suppressor protein p53. Identification of Aurora kinases as RasGAP Src homology 3 domain binding protein, also implicates these kinases as potential effectors in the Ras pathway relevant to oncogenesis. Abnormal elevated expression of Aurora kinases detected in human cancer cells could help explain the underlying biological mechanisms responsible for the development of many cellular phenotypes associated with malignant cells. Identification of these mechanisms offers the possibility of designing novel targeted therapies for cancer in the future.

Summary Prostate inflammation has been suggested as an etiology for benign prostatic hyperplasia (BPH). We show that decreased expression of the androgen receptor (AR) in luminal cells of human BPH specimens correlates with a higher degree of regional prostatic inflammation. However, the cause-and-effect relationship between the two events remains unclear. We investigated specifically whether attenuating AR activity in prostate luminal cells induces inflammation. Disrupting luminal cell AR signaling in mouse models promotes cytokine production cell-autonomously, impairs epithelial barrier function, and induces immune cell infiltration, which further augments local production of cytokines and chemokines including Il-1 and Ccl2. This inflammatory microenvironment promotes AR-independent prostatic epithelial proliferation, which can be abolished by ablating IL-1 signaling or depleting its major cellular source, the macrophages. This study demonstrates that disrupting luminal AR signaling promotes prostate inflammation, which may serve as a mechanism for resistance to androgen-targeted therapy for BPH.

Purpose: To assess the clinical significance of Aurora-A kinase, a centrosome-regulating serinethreonine kinase, in ovarian carcinoma. Experimental Design: Aurora-A kinase expression was assessed by Western blot (cell lines) or immunohistochemistry (high-grade epithelial ovarian cancers), and clinical variables were collected by retrospective chart review. Centrosome amplification was assessed by immunofluorescence in cell lines, and by immunohistochemistry in patient samples. Results: All ovarian cancer cell lines exhibited significant Aurora-A kinase protein overexpression, and all except A2780-par had centrosome amplification, a characteristic of mitotic dysregulation leading to genomic instability. Fifty-eight of 70 patient samples (82.8%) exhibited Aurora-A kinase overexpression compared with normal ovarian surface epithelium. High Aurora-A kinase expression was strongly associated with supernumerary centrosome count in tumor cells (P < 0.001). Tumors with the greatest Aurora-A overexpression (n = 24) had decreased patient survival (median survival, 1.44 versus 2.81 years; P = 0.01). High Aurora-A expression and suboptimal surgical cytoreduction remained predictors of poor survival (P < 0.05) by multivariate analysis. Conclusions: Aurora-A kinase is overexpressed by a substantial proportion of ovarian cancers and is associated with centrosome amplification and poor survival. It may be a useful prognostic marker and target in ovarian cancer.